A probe destined for the frozen edge of the solar system is due to blast off today from Cape Canaveral in Florida after its launch was delayed last night by high winds. Its mission is to rendezvous with Pluto before heading further into the unexplored fringes of our cosmic habitat.

Pluto is the only planet not to have been treated to a spaceship flyby or landing, so when the New Horizons probe zips past it will complete the set. The icy planet is a relic of the material left over from the formation of the solar system about 4.6bn years ago. Astronomers hope the trip will tell them not just about Pluto, but also about how the other planets formed.

The piano-sized probe will be lifted into space by an Atlas 5 rocket, flanked by five boosters. These will propel the 478kg spacecraft to the moon in just nine hours, a trip the Apollo astronauts made in three days. "It's leaving Earth faster than anything has ever left the planet - at about 36,000mph," said Hal Whitehead, project scientist on the mission.

The next crucial milestone in the $700m (£400m) mission will be a helping hand from Jupiter. New Horizons will slingshot around the planet early next year. The boost from the giant planet's gravity will cut the probe's journey to Pluto by four years.

When it leaves Jupiter behind, it will be cruising at 47,000mph. Even with the extra speed, however, the hook-up with Pluto is not scheduled until summer 2015.

When the probe gets there, Nasa has opted for a flyby rather than stopping for a close-up look. The problem is that Pluto's gravity is so weak that putting the brakes on would mean carrying huge amounts of fuel. This would not be practical to store on board.

After leaving the icy planet, New Horizons will check out one or two other icy, rocky blobs in the Kuiper Belt - a region of celestial junk left over from the solar system's formation. As it skips by Pluto, the probe will map the planet's surface and its moon, Charon. It will measure the surface composition, structure and the escape rate of Pluto's atmosphere. "We'll be able to map it up to football field dimensions and we'll be able to see what it really looks like. Does it have high valleys, mountains, cryogenic geysers?" said Dr Whitehead.

"Because it's so far from the sun, it has been very, very cold for its entire existence. So it's preserved the material that was there 4.6bn years ago. In that sense, it gives us a window back to the past, to the origin of the solar system."

The American astronomer Clyde Tombaugh discovered Pluto in 1930, but it has become clear that the enigmatic planet is the odd one out. It occupies an awkward, "eccentric" orbit at a 17 degree angle to the plane in which most of the other planets orbit. The round trip takes 248 Earth years, taking it from 2.8bn miles from the sun at its nearest to 4.6 bn miles away at its farthest. At times it is closer to the sun than Neptune.

Strangest of all is its moon Charon, which is close to Pluto's size. "None of the other planets have a planet-moon relationship like that," said Monica Grady, a planetary scientist at the Open University in Milton Keynes. Numerous Kuiper Belt objects orbit each other in this way though. And this raises one of the enduring debates of science: is Pluto actually a planet? On size alone, another Kuiper Belt object (2003 UB313) has to be given the planet accolade as well.

The International Astronomical Union, the Paris-based organisation that decides these things, convened a working party to discuss the issue, but they could not agree on a solution. It seems a final end to the argument will have to wait until the IAU's general assembly in the summer. "The scientists probably consider that they made a mistake not defining a planet earlier," said a spokesperson for the IAU ruefully.

Professor Grady said: "When Pluto was first found it was fair enough to call it a planet. For me it seems pretty clear that Pluto is a Kuiper Belt object. But it's teetering on the brink - a split personality."